Load Side Tap

[spinomaly]

Looking for comments on the following.

Summary: PG&E will not allow any changes to the main service panel due to violation of minimum distance from gas service. The existing panel is from 1978 and has no rating labels. Discussion here: PG&E Main Panel Clearance - Help

The solar company was going to install line side taps which was the reason for the main panel change. However, the main service panel feeds a 125A subpanel in the garage which contains all the circuits for the home. The subpanel is fed by 100A feeders from the main panel. The main panel has a 100A circuit breaker.

Why wouldn't a load side tap work in this situation? From what I have briefly read online, NEC 705.12 appears to provide regulations for this scenario. The PV could be fed into the subpanel as long as 125% of the inverter output circuit current plus the rating of the OCPD protecting the busbar is not greater than the ampacity of the busbar. If the current busbar does not have the required ampacity then I could just add a larger one protected by a 100A circuit breaker on the feeder from the main panel.

This seems to fall within the regulations(?)

 

[wwhitney]

The busbar rules in 705.12 apply to all panels between the PV inverter and the utility. So if you interconnect at a subpanel, you need to comply at both the subpanel and the service panel. You haven't provided enough information about the service panel to indicate if it would comply. If it just has a single 100A branch breaker in it, you have many options.

Cheers, Wayne

 

[spinomaly]

Thanks for the reply.

My thought is to change out the subpanel with one that has a 100A breaker fed from the main panel which also has a 100A breaker. I would keep the existing feed from the main to subpanel which is rated at 100A. The 100A breaker in the subpanel would isolate/protect any potential excess current being fed back to the existing feed and main panel. The subpanel busbar rating would be chosen such that it complies with the amperage regulation when fed from the grid and the PV.

 

[wwhitney]

That's all well and good, but then you have the service panel to contend with. In your other thread you mentioned it has two breakers, one for a pool/hot tub and this 100A breaker for the subpanel. So just two branch breakers?

What are the size of the service panel main breaker and pool/hot tub breaker?

If your neighbors have what appears to be the identical service panel, do any of those panels still have the labels on them? If so, gather that information.

Cheers, Wayne

 

[spinomaly]

The main panel has two breakers (100A each). One feeds the pool and hot tub, the other the subpanel in discussion (located in garage) which is for the house. I will need to find a neighbor with a pool.

Can you clarify what you mean by I have the service (main) panel to contend with?

 

[wwhitney]

The main panel has two breakers (100A each). One feeds the pool and hot tub, the other the subpanel in discussion (located in garage) which is for the house. I will need to find a neighbor with a pool.

Can you clarify what you mean by I have the service (main) panel to contend with?

Ah, so your service panel has no main breaker? There's no single breaker you can turn off to kill everything, you have to shut off both 100A breakers to do that?

In that case, by the usual interpretation of 705.12, you don't have to worry about the busbar in your service panel, as it is a service conductor.

If your service panel had a main breaker and then say 3 branch breakers, then it too would have to comply with 705.12, which is what I meant.

Cheers, Wayne

P.S. The simplest way to interconnect PV+ESS in the above configuration is to ensure you have a main breaker in your garage subpanel, and then to intercept the 100A feeder to that garage panel for a feeder interconnection under 2020 NEC 705.12(B)(1).

 

[spinomaly]

Yes. To shut off all power (pool, hot tub, house) would require shutting off both breakers.

What you describe is what I am also thinking. Change out the subpanel in the garage with one that has a main breaker and then follow NEC 705.12(B).

The solar company also stated that the city is requiring a main panel update for any major electrical changes. I am going to call them today and explain this scenario which should not impact the service panel.

Really appreciate the quick replies.